This invention relates to a novel method for conditioning partially-completed cathode-ray-tube bulb assemblies for long-term storage and/or for transit to their final assembly plant.
A shadow-mask color-television picture tube is prepared by steps including (a) producing a luminescent-screen structure upon the inner surface of a faceplate panel, (b) heat-sealing the panel to the large opening of a funnel, (c) heat-sealing a mount assembly to the small opening of said funnel, and then (d) exhausting and sealing the tube. In some situations, it is desired to store for a relatively long term; e.g., three to thirty days, the partially-completed assembly as it exists after step (b). In other situations, it is desired to ship such partially-completed assemblies to distant manufacturing plants; e.g., a hundred to three thousand miles away, which may require relatively long transit time. In both situations, the assembly may be and usually is subjected to fluctuations in temperature and humidity.
Some tubes have screen structures comprising a layer of aluminum metal in contact with a layer of carbon particles, which may be either crystalline, such as graphite, or may be amorphous, such as lamp black. The carbon layer may be employed on the viewing side of the screen structure as a lightabsorbing matrix as described, for example, in U.S. Pat. No. 3,558,310 to E. E. Mayaud, and/or on the gun side of the screen structure as a heat-absorbing layer as described, for example, in U.S. Pat. No. 3,703,401 to S. B. Deal et al. In either or both type structures, the aluminum metal layer is progressively degraded in conductivity and reflectance by conversion to aluminum compounds when the layer is exposed for any extended term to normal ambient water-vapor concentrations in excess of about 2500 ppm (parts water vapor per million parts gas), which corresponds to the dew point of about +12.degree.F. The degradation starts at random points on the aluminum layer and spreads outwardly therefrom. Even when only small areas of the aluminum layer are degraded in this manner, the tube is rendered unsalable.
In solving a different problem, U.S. Pat. No. 3,650,401 to J. A. Files suggest flushing the bulb assembly with a dry (dew point -22.degree.F or -30.degree.C) noncontaminating gas soon after heat sealing the panel to the funnel, and then capping the bulb assembly with a temporary closure. Such prior process has been found to retard the degradation of the aluminum metal layer where there is no carbon layer present. But, where a carbon layer contacts the aluminum metal layer, this treatment is effective for only a short period of time.